Hydroformylation, discovered by Roelen in 1938, has been the largest homogeneous catalytic process in industry. More than 15 billion pounds of aldehydes and alcohols per year have been produced based on Fe, Zn, Mn, Co, Cu, Ag, Ni, Pt, Pd, Rh, Ru and Ir based catalysts. In these processes, achieving high selectivity to linear products is extremely important for commercial application. Despite the extensive investigation by both academic and industrial groups such as BASF, Dow, Shell and Eastman, among others, there still remain fundamental and practical problems regarding selectivity. New concepts for controlling selectivities are very important in catalytic reactions. Highly efficient selective catalysts will allow some bulky chemicals to be produced in an environmentally sound manner under milder conditions.
Cobalt catalysts (e.g., HCo(CO)4) dominated industrial hydroformylation until rhodium catalysts (e.g., HRh(CO)2(PPh3)3) were introduced in earlier 1970's. In 2004, it is estimated that approximately 75% of all hydroformylation processes were based on rhodium triarylphosphine catalysts. Achieving high regioselectivity to linear aldehydes is critical for hydroformylation and related reactions. The resulting aldehydes are converted to alcohols, carboxylic acids or other derivatives, which are used as plasticizers, detergents, surfactants, solvents, lubricants and chemical intermediates.
Scheme 1 below shows the dissociation of a Rh catalyzed hydroformylation catalyst.

The successful commercialization of HRh(CO)(PPh3)2 technology has been based on the key discovery of Pruett at Union Carbide and Booth at Union oil that the use of rhodium with excess phosphine ligand can lead to forming active, selective hydroformylation catalysts. The need for excess phosphines is due to the facile Rh—PPh3 dissociation in the catalytic system as illustrated by Scheme 1. Loss of PPh3 from HRh(CO)(PPh3)2 results in more active, but less regioselective hydroformylation catalysts B and C. In the commercial process, up to an 820 fold excess of PPh3 to Rh is used to assure high linear:branch selectivity ratio, i.e., up to 17:1, for the hydroformylation of 1-hexene. Commercial hydroformylation of propylene has been run with a 400 fold excess of PPh3 to Rh with a linear:branch selectivity ratio of 8-9:1 being achieved.
Rh/PPh3 catalyzed hydroformylation is the key for making all oxo alcohols. Propylene is the largest single alkene hydroformylated to produce butylaldehyde, which can be hydrogenated to produce butanol, or dimerized by an aldol condensation and then hydrogenated to form 2-ethyl-1-hexanol, the largest single product produced by hydroformylation (over 5 billion lbs a year). 2-ethyl-1-hexanol is usually reacted with phthalic anhydride to produce dialkyl phthalic esters that are used as plasticizers to keep polyvinyl chloride plastics soft and flexible.
In the hydroformylation process, it is critical to get cheaper feed stocks for starting materials. For example, internal higher alkenes (SHOP alkenes) such as 3-octenes are desirable for converting the alkenes to linear aldehydes. Direct use of raffinate II (a mixture of n-butenes/butanes) and 1-butene and 2-butene mixtures are useful for hydroformylation. For hydroformylation of n-alkenes, it is important to obtain high linear selectivity. Hydroformylation of allylic alcohol and subsequent reduction can lead to 1, 4 butenol. Functionalized internal alkenes can be used as alternative routes to bifunctional building blocks for polymers. Hydroformylation of methyl-3-pentenoate leads to making starting materials for polyamides and polyesters. In the tandem-isomerization and hydroformylation processes, high isomerization rates combined with high selectivity towards terminal aldehydes are desirable with minimized undesirable hydrogenation reactions and minimum isomerization towards conjugated compounds.
To overcome the need of using large excess of phosphines in the hydroformylation processes and achieve high regioselectivity, a new generation of transition metal catalysts were developed using bisphosphine ligands. For example: Bisbi by Eastman Chemical; Xantphos by Prof. Leeuwen (University of Amsterdam), Bernhard Breit, Acc. Chem. Res. 2003, 36, 264-275, Bernhard Breit, Wolfgang Seiche, Synthesis 2001, 1, 1-36); and UC-44 by Union Carbide. These ligands are illustrated below.
By using these ligands, a typical 400 fold excess of PPh3 has been reduced to a 5 fold excess of chelating phosphines. This new generation of chelating phosphines has led to high linear:branched ratios as well as to higher catalytic activities. For example, a linear to branch ratio of 70-120:1 for hydroformylation of 1-hexene has been observed. Casey and van Leeuwen proposed that part of regioselectivity in the Rh-catalyzed hydroformylation is due to metal bisphosphine bite angle around 120 degree is formed, i.e., “the Bite angle hypothesis” as illustrated below.

Despite that a number of chiral bisphosphorus ligands being used as catalysts for hydroformylation and related reactions, the highly selective, active phosphorus ligands for hydroformylation still remain an area of strong research interest. However, because of the dissociation of phosphines from the Rh—CO coordination, is a problem for achieving high regioselectivity, that is high linear to branch ratios of the products produced. Developing families of phosphorus ligands with multi-chelating coordination modes is attractive. The tetraphosphorous ligands of the present invention, because of their coordinating abilities through multi-chelating coordination modes, lead to highly regioselective transition in metal-ligand catalyzed hydroformylation and related reactions to provide high linear to branch ratios than those previously obtained. Also, the symmetric nature of these ligands allows these ligands to be prepared easily.